The present invention relates, in general, to myocardial hypertrophy and, in particular, to agents that inhibit cardiac Gq-coupled receptor signaling and to methods of inhibiting myocardial hypertrophy using same.
Myocardial hypertrophy is an adaptive response to a variety of mechanical and hormonal stimuli and represents an initial step in the pathogenesis of many cardiac diseases which ultimately progress to ventricular failure. Due to the high mortality associated with heart failure, there is strong interest in identifying regulatory molecular determinants which lead to myocardial hypertrophy and subsequently to the transition to failure. Several disease conditions can trigger the non-failing ventricle to develop increased wall thickness as an initial compensatory mechanism to meet the heightened demands placed on the pump. In man, this situation can arise in some cardiovascular disease states including hypertension. The mechanisms by which cardiac hypertrophy is initiated and how this condition eventually progresses to heart failure are poorly understood.
The heart is unique in that it is composed of terminally differentiated myocytes which respond to hypertrophic stimuli by increasing in size rather than number (Chien et al, FASEB J. 5:3037 (1991)). Utilizing cultured neonatal cardiac myocytes, several independent signaling pathways have been implicated in the activation of the hypertrophic response in vitro (Chien et al. FASEB J. 5:3037 (1991). The hypertrophy seen in vitro involves an increase in cellular size and volume, differential expression of various contractile proteins, and reactivation of an embryonic gene program which includes ventricular induction of atrial natriuretic factor (ANF), skeletal a-actin, and b-myosin heavy chain. Candidate signaling molecules for the initiation of hypertrophy have been identified including p21ras (ras) (Thorburn et al, J. Biol. Chem. 268:2244 (1993)), although hypertrophy of myocytes in vitro can also occur in a ras-independent manner (LaMorte et al, J. Biol. Chem. 269:13490(1994)). The heterotrimeric guanine nucleotide binding (G) protein, Gq, is thought to be important in this process since various ligands (i.e. phenylephrine, angiotensin II, and endothelin I) that activate Gq-coupled receptor molecules can trigger hypertrophic responses in cultured myocytes (Sadoshima et al, Cell 95:977 (1993), Simpson, J. Clin. Invest. 72:732 (1983); Shubeita et al, J. Biol. Chem. 265:20555 (1990)).
Receptors that stimulate Gq are members of the G protein-coupled receptor family which share conserved seven transmembrane topography. The binding of agonists induces conformational changes in the receptor molecule which cause its intracellular domains to interact with the carboxyl terminal portion of the a-subunit of G proteins (Neer et al, Cell 80:249 (1995)). It has been previously reported that cellular expression of the third intracellular domain (3i) of the a1B-adrenergic receptor (AR) in vitro antagonizes a1B-AR-mediated signal transduction, apparently through competition between the 3i peptide and the activated receptor for binding sites on Gaq (Luttrell et al, Science 259:1453 (1993)). Other in vitro studies have demonstrated that peptides derived from the carboxyl terminus of Gas (Palm et al. FEBS Lett. 261:294 (1990)) and Gai2 (Okamato et al, J. Biol. Chem. 269:13756 (1994)) can block in vitro receptor-mediated G protein signaling.
The present invention results from studies demonstrating, in vivo, the importance of myocardial Gq-coupled signaling in the initiation of ventricular hypertrophy. This demonstration makes possible novel therapeutic strategies for preventing hypertrophy and the transition to heart failure.
The present invention relates to agents that inhibit cardiac Gq-coupled receptor signaling. The invention further relates to a method of inhibiting maladaptive ventricular hypertrophy associated with various forms of cardiac disease in transition to failure, which method utilizes such agents. The invention further relates to a method of inhibiting vascular smooth muscle proliferation and migration, which method also utilizes inhibitors of Gq-coupled receptor signaling.
Objects and advantages of the invention will be clear from the description that follows.